Surface grafting of a π-conjugated amino-ferrocifen drug

The electrochemical grafting of a π-conjugated amino-ferrocifen complex (1) at gold surfaces may be achieved through the direct electrochemical oxidation of the amino group (+0.9 V/SCE) but is prone to proceed also indirectly through the oxidation of the ferrocene moiety (+0.45 V). The modification and characterization of the gold electrode surfaces are demonstrated by cyclic voltammetry, ellipsometry, Infra-Red Reflection–Absorption Spectroscopy (IRRAS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and X-ray Photoelectron Spectroscopy (XPS). Combination of these techniques clearly demonstrates that (1) is covalently attached to the gold surfaces via an AuNH bond. The crucial role played by the electrogenerated aminyl radical in the grafting process is highlighted. This transient species, which is responsible for the covalent grafting of (1) onto the gold surface was also found able to react with the amino-ferrocifen parent complex to form multilayers. This detailed characterization of the grafted electrode surface finally brings insight into the overall mechanistic frame related to the grafting of conjugated amino compounds and, consequently, allowing establishing definitively the occurrence of the intramolecular redox catalysis process which is key to their cytotoxic properties against cancer cells.